The invention relates generally to the field of agricultural machines and, more particularly, concerns a device for the adjustment and control of hydraulic cylinders on front attachments and assemblies of work machines such as self-propelled agricultural machines.
The use of hydraulic or pneumatic work cylinders on machines and devices for producing a rectilinear movement is already generally known. By means of these linear motors very high speed reductions and considerable lifting or adjusting forces can be achieved.
For example DE 36 28 472 C2 shows a work machine with a work attachment of adjustable height which is removably coupled to the work machine using a hydraulic cylinder. By means of the hydraulic cylinder the weight of the work attachment is transmitted to the work machine and at the same time the implement is moved to the desired working position. It is the aim of this patent to reduce the digging and bearing forces of the work attachment as a function of the conditions of use and the presetable values for the bearing or load relief pressure. On the circuitry side the work cylinders are connected by a 3/2-port directional control valve to a hydraulic pump, wherein in the pressure line between the directional control valve and the hydraulic cylinder is located a pressure sensor which is connected by a control line to a pressure control circuit with a setpoint generator. By a further control line the pressure control circuit is connected to a regulating valve which is arranged in a bypass line connecting the pressure line to the return line. By means of this circuit arrangement the actual pressure value prevailing in the hydraulic cylinder can be regulated to reduce the bearing forces of the front work attachment or the load relief pressure can be regulated in case of deviations from a nominal pressure value set in the control device.
An advantageous development of this type of control system is the subject of EP 0 610 900 A1. To improve the prior-art load relief device, a rechargeable pressure storage device with a switching valve in front is connected to the pressure chamber of the piston face of the hydraulic cylinder and a further switching valve is provided between the pressure and return lines for the hydraulic fluid. By means of this switching valve assembly, after reaching the pressure necessary for the load relief mode in the pressure chamber of the hydraulic cylinder and in the rechargeable pressure storage device, the hydraulic circuit on the motor vehicle side can be separated from the load relief circuit, the pressure storage device remaining connected to the pressure chamber of the hydraulic cylinder for maintaining the load relief mode. In case of variations in load relief pressure which are above or below the set nominal value, the line connection of the pressure chamber of the hydraulic cylinder and of the pressure storage device to the pressure or return line is made automatically by the switching valve assembly.
A hydraulic floating assembly for an agricultural implement is known from DE 33 37 789 A1. According to this patent publication the pressure chambers of the hydraulic cylinders are connected by a directional control valve to a hydraulic pump, and in the branch of the high-pressure line between the directional control valve and the pressure chambers of the hydraulic cylinders is inserted a pressure storage device with a further cylinder in front having a floating piston. With this hydraulic floating assembly, front harvesting or work attachments on self-propelled machines are kept at a yielding pretensioning force which is adjustable as a function of their weight in such a way that they can glide over the ground and on encountering an obstacle are lifted, assisted by the pressure forces existing in the pressure storage device.
For the resilient suspension of vehicle axles with damped vibrations, from vehicle construction are non-analogous solutions in which the load-bearing vehicle axles are arranged in a pivotably mounted wishbone provided directly on the vehicle frame (e.g. DE 14 80 154; DE 24 07 970; and DE 28 11 873) or in a rocker arm which is linked to a longitudinal member mounted at the end on the vehicle frame (e.g. DE 10 92 778). The wishbones mounted directly on the vehicle frame or the longitudinal member mounted on the vehicle frame are connected to a hydraulic or pneumatic cylinder. Due to the rotatable arrangement of wishbone and longitudinal member and their cooperation with a pneumatic gas strut or a pneumatic/hydraulic cylinder, the vibrations and impacts which arise during automotive operation and are transmitted from the wheel carriage to the whole vehicle are largely compensated or damped and, with improved ground adhesion of the vehicle wheels, good adaptation of the wheel carriage to the road or highway is achieved.
The application or direct transfer of these basic solutions is not possible for reasons discussed below.
Depending on the crop, self-propelled harvesting machines are equipped with different front harvesting attachments. Inevitably there are great differences in weight between these different front harvesting attachments. For lifting and lowering the different front harvesting attachments and for producing an adjustable yielding pretensioning force in the lifting and adjusting cylinders for maintaining a floating arrangement of the implements during the harvesting operation, relatively extensive equipment must be provided on the hydraulic side.
Particularly extreme are the differences in weight with the front harvesting attachments for self-propelled forage harvesters. For the front harvesting attachments which are used for example for harvesting grass with a pick-up, working pressures of approximately 40 bars are necessary, while in corn harvesting with a front corn harvesting attachment pressures of up to 130 bars must be applied. For the connection of front harvesting attachments with a relatively high weight to self-propelled harvesting machines, there are provided cylinders in addition to the already existing hydraulic lifting and adjusting cylinders. These additional cylinders are dismantled again for operations with front harvesting attachments having a relatively low weight.
The different load states of a harvesting machine also include the degree of loading, the field condition and the function, which require differentiated adjustment of the front harvesting attachments and wheel carriages by altered, differing work pressures in the hydraulic cylinders. This is to ensure trouble-free operation with a high assurance of control, a high machine output and very low harvesting losses. Thus greatly varying axle loads have to be taken up and transmitted to the road or path from the wheel carriage when travelling empty with a front harvesting attachment hooked on, as opposed to when travelling with a fully loaded grain bin.
Inevitably a change in travelling state occurs with harvesting processes on more or less level field surfaces as opposed to harvesting of crops on slopes. For example, the left and right wheel carriages of the machine is subjected to different loads under these different field conditions.
By contrast when working with a front harvesting attachment mounted permanently on the harvesting machine, the spring travel of the wheel carriage must be as short as possible or completely blocked.
With the devices known from the state of the art and mentioned above, however, the problems arising from the varying operating and working conditions of self-propelled harvesting machines cannot be solved.
It is therefore an object of the present invention to overcome one or more of the difficulties described above.
It is another object to develop a device which, with automatic regulation of the chosen setting by an electronic machine control system, allows adjustment and control of the work cylinders provided on front work attachments and machine assemblies as a function of the constantly changing, different states of loading and operation.